The present invention relates to a system for controlling the operation of an automotive engine, and more particularly to a learning control system for updating data stored in a table for controlling the fuel supply in an electronic fuel-injection system.
In one type of electronic fuel-injection control, for example the publication Japanese Patent Application Laid Open No. 57-122135, the amount of fuel to be injected into the engine is determined in accordance with engine operating variables such as mass air flow, engine speed and engine load. The amount of fuel is decided by a fuel injector energization time (injection pulse width). Basic injection pulse width (T.sub.p) can be obtained by the following formula. EQU T.sub.p =K.times.Q/N (1)
where Q is mass air flow, N is engine speed, and K is a constant.
Desired injection pulse width (T.sub.i) is obtained by correcting the basic injection pulse (T.sub.p) with engine operating variables. The following is an example of a formula for computing the desired injection pulse width. EQU T.sub.i =T.sub.p .times.(COEF).alpha..times.K.sub.a ( 2)
Where COEF is a coefficient obtained by adding various correction or compensation coefficients such as coefficients of coolant temperature, full throttle open, engine load, etc., .alpha. is a .lambda. correcting coefficient (the integral of the feedback signal of an O.sub.2 -sensor provided in an exhaust passage), and K.sub.a is a correcting coefficient by learning (hereinafter called the learning control coefficient). Coefficients, such as the coolant temperature coefficient and engine load, are obtained by looking them up in tables in accordance with sensed information. The value of the learning control coefficient K.sub.a is obtained from a K.sub.a -table in accordance with engine load. All of the coefficients K.sub.a stored in the K.sub.a -table are initially set to the same value, that is the number "1". This is caused by the fact that the fuel supply system is to be designed to provide the most proper amount of fuel without the coefficient K.sub.a. However, very automobile can not be manufactured to have a desired function, resulting in the same result. Accordingly, the coefficient K.sub.a should be updated by learning in every automobile when it is actually used. If the difference between the initial value "1 " and the updated value is large, hunting of the fuel injection system occurs. Heretofore, in order to prevent such a hunting, the initial value is incremented or decremented little by little until the value is entirely rewritten. Accordingly, a long time elapses before the value is updated, causing the delay of fuel control (FIG. 6a).